A known ignition timing control system which advances the spark in the lower range of the idling domain is described, for example, in the German laid-open application OS No. 2,807,499. In the system described there, any additional loads placed on the engine in the idling domain, for example by connection of electrical loads, cause the engine speed to decrease still further. Accordingly, the increasing degree of spark advance provided by the known system counteracts the rpm drop and produces an overall stabilization of the idling speed of the engine. Because the spark advance cannot be increased indefinitely, a provision is made to return the ignition timing to its original normal setting when the engine speed falls below a selectable value which preferably lies below even the lowest engine idling speed. It is a disadvantage of the known system that the spark advance also becomes effective as the engine accelerates from speeds below the lower threshold, i.e., when the engine is being started up. This sudden change in the ignition timing causes misfires and rough engine operation. Accordingly, the overall engine characteristics during starting are affected adversely.